Problems of tree building
As evolution only occurred once, of all the possible trees only one is therefore correct. "The perfect phylogenetic tree will never be constructed" (Majerus et al 1996). The science of systematics is currently very active and new research elucidates new theories as well supporting more traditional. There are countless controversies and current opinion changes rapidly. Building large-scale phylogenetic trees is consequently a challenging process and any therefore a tree, such as that available on this site, will constantly require updating.
There is no way of testing the accuracy of a tree of life, but by using various techniques (such as bootstrapping) it is possible to hypothesise the relaibility of specific branching positions and sequences within a tree.